eccrypto.generatePrivate() (#38)

* eccrypto.generatePrivate()

* Fix comment indentation

README.md

@@ -43,7 +43,7 @@ var crypto = require("crypto");
 var eccrypto = require("eccrypto");
 
 // A new random 32-byte private key.
-var privateKey = crypto.randomBytes(32);
+var privateKey = eccrypto.generatePrivate();
 // Corresponding uncompressed (65-byte) public key.
 var publicKey = eccrypto.getPublic(privateKey);
 
@@ -64,12 +64,11 @@ eccrypto.sign(privateKey, msg).then(function(sig) {
 ### ECDH
 
 ```js
-var crypto = require("crypto");
 var eccrypto = require("eccrypto");
 
-var privateKeyA = crypto.randomBytes(32);
+var privateKeyA = eccrypto.generatePrivate();
 var publicKeyA = eccrypto.getPublic(privateKeyA);
-var privateKeyB = crypto.randomBytes(32);
+var privateKeyB = eccrypto.generatePrivate();
 var publicKeyB = eccrypto.getPublic(privateKeyB);
 
 eccrypto.derive(privateKeyA, publicKeyB).then(function(sharedKey1) {
@@ -82,12 +81,11 @@ eccrypto.derive(privateKeyA, publicKeyB).then(function(sharedKey1) {
 ### ECIES
 
 ```js
-var crypto = require("crypto");
 var eccrypto = require("eccrypto");
 
-var privateKeyA = crypto.randomBytes(32);
+var privateKeyA = eccrypto.generatePrivate();
 var publicKeyA = eccrypto.getPublic(privateKeyA);
-var privateKeyB = crypto.randomBytes(32);
+var privateKeyB = eccrypto.generatePrivate();
 var publicKeyB = eccrypto.getPublic(privateKeyB);
 
 // Encrypting the message for B.

browser.js

@@ -112,6 +112,20 @@ function hmacSha256Verify(key, msg, sig) {
   });
 }
 
+/**
+  * Generate a new valid private key. Will use the window.crypto or window.msCrypto as source
+  * depending on your browser.
+  * @return {Buffer} A 32-byte private key.
+  * @function
+  */
+exports.generatePrivate = function () {
+  var privateKey = randomBytes(32);
+  while (!isValidPrivateKey(privateKey)) {
+    privateKey = randomBytes(32);
+  }
+  return privateKey;
+};
+
 var getPublic = exports.getPublic = function(privateKey) {
   // This function has sync API so we throw an error immediately.
   assert(privateKey.length === 32, "Bad private key");

index.js

@@ -91,6 +91,19 @@ function pad32(msg){
   }
 }
 
+/**
+ * Generate a new valid private key. Will use crypto.randomBytes as source.
+ * @return {Buffer} A 32-byte private key.
+ * @function
+ */
+exports.generatePrivate = function() {
+  var privateKey = crypto.randomBytes(32);
+  while (!isValidPrivateKey(privateKey)) {
+    privateKey = crypto.randomBytes(32);
+  }
+  return privateKey;
+};
+
 /**
  * Compute the public key for a given private key.
  * @param {Buffer} privateKey - A 32-byte private key

test.js

@@ -235,6 +235,17 @@ describe("ECIES", function() {
     });
   });
 
+  it("should encrypt and decrypt with generated private and public key", function () {
+    var privateKey = eccrypto.generatePrivate();
+    var publicKey = eccrypto.getPublic(privateKey);
+    return eccrypto.encrypt(publicKey, Buffer.from("generated private key"))
+        .then(function(enc) { return eccrypto.decrypt(privateKey, enc); })
+        .then(function(msg) {
+          expect(msg.toString()).to.equal("generated private key");
+        });
+  });
+
+
   it("should reject promise on bad private key when decrypting", function(done) {
     eccrypto.encrypt(publicKeyA, Buffer.from("test")).then(function(enc) {
       eccrypto.decrypt(privateKeyB, enc).catch(function() {